[ARC5] SCR274 field test

[J Mcvey via ARC5]

I was trying to avoid needing to run the engine while operating for only a few hours at a clip.
I also was not aware (since I never did the experiment) that the battery will drop as low as 8 or 9 while cranking the engine, so maybe 11 volts at the battery isn't so bad after all.
As far as I know, lead/acid batteries can also be "quick checked" by their no load "resting voltage" several hours after charging. It should be at least 12.6V.The deep cycle was pulled fresh off of my trickle charger. In rx mode and tx dyno running, it reads 12.6v. When keying the transmitter it sagged to 11v . The Jeep had been sitting for about a week and a half , so it's resting voltage was 12.2v which indicates a partial discharge state. 
Both are the "sealed" type with no access to the cells.

Some here are saying that it's the "light" cable., but that series resistance would only be a problem in wire heat loss and a drop at the dyno end, not at the battery! A resistive cable would actually DECREASE the current draw.

Yes the power cable should be beefier, but sometimes i have to work with what I have laying around.Doing the the math at 30 amps for my 6 foot length, considering 12 ft total.#12 is about 1.58 ohms. 12 ft is 19 X 10^-3 ohms. Even at 30 amps the drop is  only 560 millivolts. Under actual operating conditions, it will be much less.
Now that think about it, my 100W ft 450 will drop the battery voltage in tx as well. I guess the load resistance starts to rival the internal battery resistance, but I don't think it got to 11V, though. maybe 11.6 or so... I need to revisit this...
Someone asked if I resoled the deselected Tx  current draw problem. Yes, I described my findings in that thread as I always do if I have any. We are all here to help and learn things along the way, so if a solution is found it should be shared with the group. Unfortunately, this is NOT the case all too often in many forums. I try to be part of the solution rather than part of the problem...



     On Sunday, July 19, 2015 9:00 AM, Bill Cromwell <wrcromwell at gmail.com> wrote:
   

 Hi J,

You have answered the question about where your measurements were taken 
and the wire gauge to the dynamotors. You haven't said anything about 
the engine running or not. Try measuring the battery terminal voltage 
while you are cranking the engine. V-8 engines can drop that to 8 or 9 
volts! Those batteries have internal resistance that changes with the 
state of the charge (higher internal resistance when discharged).

Your cranking battery is designed for those high surge currents like 
starting the engine. But it won't tolerate being deeply discharged at 
all. How old, what condition, and what charge state was that battery? 
How do you know?

Deep cycle batteries have traded the high surge current capability for 
the 'deep discharge cycle' capability. They have a higher internal 
resistance (which gets higher as the battery discharges). You can expect 
a lower terminal voltage with a higher current draw, especially with 
high surge currents. What was the age, condition, and charge state of 
that battery when you tested it? How do you know?

The 'how do you know' questions have their answers in measurements of 
the specific gravity of the electrolyte and load tests to compare them 
to manufacturer's specifications. Sulphated and contaminated plates will 
reduce the energy available. So will *any* corrosion in the terminals 
(between the posts and connector).

Good luck with your project. I hope the solution to your problems is 
resolved by starting the engine.

73,

Bill



On 07/18/2015 08:28 PM, J Mcvey via ARC5 wrote:
> I was hoping that I could run the dual rx/tx setup off of my  jeep battery, but it seems it needs a stiffer deep cycle type to keep up with the load in transmit. The jeep batter sagged badly and for that matter so did the deep cycle battery (11v under full load), but it was sufficient to keep things working.
> I think i'm missing something about the nature of dynamotors and batteries ...
> With the two transmitter filaments ( 4X 1625) @ 2a and the rx pulling about 2.5a, that's a constant 4.5a, add the dyno in stanby which bring the the total cw break-in receive mode 7.5a.
> The dyno says 9a @ 12V continuous duty for 440v @ 200 ma .That should be a max of 16.5a a key down. So how can 16.5 amps draw a 130AH battery down to 11v from it's fully charged resting voltage of 12.6v ? ( it recovers on key up)
> When I was using a SMPS, it sounded good, now I've got some chirp due to power droop.What say you experts?
> BTW, I was doing this in "original spec" using a very short wire antenna of about 35 feet on 80 meters in NVIS config. Loads right up at about 50% inductance with coupling also about 50%. I like to stick a NE-2 ( leads shorted together) in the antenna clip on the bc-442 to see how bright I can make it glow. It tracks well with antenna current.
>

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